Electric and electronic part copper alloy sheet with excellent bending workability and stress relaxation resistance

ABSTRACT

An electric and electronic part copper alloy sheet with excellent bending workability and stress relaxation resistance is made from a copper alloy containing 1.5 to 4.0 percent by mass of Ni, Si satisfying a Ni/Si mass ratio of 4.0 to 5.0, 0.01 to 1.3 percent by mass of Sn, and the remainder composed of copper and incidental impurities, wherein the average crystal grain size is 5 to 20 μm, the standard deviation of the crystal grain size satisfies 2σ&lt;10 μm, and the proportion of the number of particles having a particle diameter of 90 to 300 nm in Ni—Si dispersed particles having a particle diameter of 30 to 300 nm is 20% or more, where the particles are observed in a cross-section defined by a direction perpendicular to a sheet surface and a direction parallel to a rolling direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an copper alloy sheet used for electricand electronic parts, e.g., terminal-connectors and relays, materialsfor semiconductors (lead frames, heat sinks), materials for electriccircuits (automobile junction blocks, consumer electric part circuits),and the like.

2. Description of the Related Art

In an automobile field, many electric and electronic parts have becomemounted in order to comply with environmental regulation and pursuit thecomfortableness and the safety, and narrowing pitches andminiaturization have been required of terminal-connectors, relays, andthe like employed. In addition, the same have been required ininformation communications and consumer-oriented fields. Consequently,materials having higher 0.2% proof stress, electrical conductivity,bending workability, stress relaxation resistance have been required aselectric and electronic part copper alloy sheets.

The 0.2% proof stress refers to a force required for inducing 0.2% ofplastic deformation of the material. If the 0.2% proof stress is high,it is possible to keep contact while a strong force is applied to acontact point. Furthermore, the same contact pressure can be obtained bya small sheet width or a thin sheet.

The electrical conductivity refers to ease of passing of electricity andis represented by a ratio (% IACS), where the electrical conductivity ofpure copper (IACS) is specified to be 100%. The electrical conductivityand the volume resistivity (μΩ·cm) are in inverse proportion. In copperalloy whose electrical conductivity is high, the volume resistivity islow, and Joule heat generation can be suppressed.

The bending workability is evaluated by the ratio (R/t) of the minimumbend radius R, at which cracking does not occur, to the sheet thicknesst. A material having good bending workability contributes tostabilization of the quality and, in addition, improves the designflexibility in pressing. Severe bending has been performed with a bendline perpendicular to a rolling direction (G.W.) previously. However,cases in which bending is performed with a bend line parallel to arolling direction (B.W.) have increased because of diversification indesign technique.

The stress relaxation resistance refers to the durability to aphenomenon in which the contact pressure is reduced with time under ahigh-temperature environment, that is, stress relaxation. The stressrelaxation resistance is indicated by a stress relaxation ratio or aresidual stress expressed in “%” after holding under predetermined loadstress, temperature, and time conditions. A material having good stressrelaxation resistance can be used, for example, in the vicinity of anautomobile engine room and, therefore, contributes to improvements indesign flexibility and reliability of electric equipment to a greatextent.

A Cu—Ni—Si base copper alloy has all of these characteristics and iswidely used as electric and electronic part copper alloy sheets atpresent. The Cu—Ni—Si base alloy is an alloy having increased 0.2% proofstress and electrical conductivity by aging precipitation of a Ni—Sicompound from a supersaturated solid solution. In the case where theCu—Ni—Si base alloy is subjected to a high-temperature short-time heattreatment referred to as a solution treatment, a recrystallized grainstructure can be formed. The bending workability of a material having arecrystallized grain structure is considerably improved as compared withthe bending workability of a material having a worked structure.

In addition, the Cu—Ni—Si base alloy is a precipitation strengtheningalloy and, therefore, can obtain a high 0.2% proof stress while theworking strain is kept at a low level as compared with a solutionstrengthening alloy in the related art. If much working strain isaccumulated, dislocation in a material structure is relaxed easily, andthe stress relaxation resistance is degraded. That is, the Cu—Ni—Si basealloy is superior to other alloy systems in the stress relaxationresistance as well.

Meanwhile, there is a so-called trade-off relationship in which if anyone of the characteristics of the 0.2% proof stress, the electricalconductivity, the bending workability, and the stress relaxationresistance of the above-described Cu—Ni—Si base alloy is furtherimproved, the other characteristics are degraded. Consequently, in manycases, improvements of the characteristics are prevented. It isparticularly difficult to ensure compatibility between the bendingworkability and the stress relaxation resistance because the bendingworkability becomes good when the crystal grain size is small and thestress relaxation resistance becomes good when the crystal grain size islarge. Therefore, there is a previously proposed technique in which thebending workability is improved mainly by controlling the crystal grainsize and the stress relaxation resistance is improved mainly by addingan element or elements.

In Japanese Patent Application Publication No. 2008-75152, JapanesePatent Application Publication No. 2008-196042, Japanese PatentApplication Publication No. 2008-266783, Japanese Patent ApplicationPublication No. 2007-146293, and Japanese Patent Application PublicationNo. 11-335756 disclose methods for improving the bending workability orthe stress relaxation resistance of Cu—Ni—Si base copper alloys. Amongthem, Japanese Patent Application Publication No. 2008-75152, JapanesePatent Application Publication No. 2008-196042, and Japanese PatentApplication Publication No. 2008-266783 disclose methods for improvingthe bending workability of the Cu—Ni—Si base copper alloys bycontrolling the crystal grain sizes. Japanese Patent ApplicationPublication No. 2007-146293 discloses a method for improving the stressrelaxation resistance of the Cu—Ni—Si base copper alloy by controllingadditional elements. Unexamined Patent Application Publication No.11-335756 discloses a method for improving the stress relaxationresistance by controlling additional elements and improving the bendingworkability by controlling the crystal grain size.

As shown in the above-described five patent literatures, the bendingworkability of the Cu—Ni—Si base alloy has been improved mainly bycontrolling the crystal grain size and the stress relaxation resistancehas been improved mainly by controlling the addition of elements.However, there are problems in that an improvement in bendingworkability by control of the crystal grain size, specifically,reduction in the crystal grain size, is accompanied by degradation instress relaxation resistance, and an improvement in stress relaxationresistance by the additional elements is accompanied by degradation inelectrical conductivity and bending workability, although not describedin the above-described five patent literatures. In addition, in order toobtain predetermined bending workability and stress relaxationresistance, it is required that the crystal grain size falls within apredetermined range through the recrystallization by a solutiontreatment. However, there is a problem in that crystal grains becomecoarse sharply in accordance with changes in treatment temperaturedepending on a desired crystal grain size and variations occur in thecharacteristics of a product.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anelectric and electronic part copper alloy sheet with excellent bendingworkability and excellent stress relaxation resistance by using aCu—Ni—Si base copper alloy.

The present inventors performed experiments on Cu—Ni—Si base copperalloy sheets, where working and heat treatment conditions were changedvariously. As a result, it was found that there was a region in whichthe form of cracking generated in bending changed from transgranularcracking to intergranular cracking along with growth of recrystallizedgrains. Furthermore, it was found that changes in dimension ofrecrystallized grain in accordance with changes in solution treatmenttemperature are different depending on the distribution state ofdispersed particles. Consequently, a copper alloy, according to thepresent invention, with excellent bending workability and stressrelaxation resistance was reached by controlling an appropriate crystalgrain size stably.

An electric and electronic part copper alloy sheet according to thepresent invention is made from a copper alloy containing 1.5 to 4.0percent by mass of Ni, Si satisfying a Ni/Si mass ratio of 4.0 to 5.0,0.01 to 1.3 percent by mass of Sn, and the remainder composed of copperand incidental impurities, wherein the average crystal grain size is 5to 20 μm, the standard deviation of the crystal grain size satisfies2σ<10 μm, and the proportion of the number of particles having aparticle diameter of 90 to 300 nm in Ni—Si dispersed particles having aparticle diameter of 30 to 300 nm is 20% or more, where the particlesare observed in a cross-section defined by a direction perpendicular toa sheet surface and a direction parallel to a rolling direction, and isexcellent in bending workability and stress relaxation resistance.

It is desirable that, in the above-described copper alloy sheet, theproportion of the number of particles having a particle diameter of 120to 300 nm in dispersed particles having a particle diameter of 30 to 300nm be 30% or more, where the particles are observed in theabove-described cross-section, (in the above-described range, theproportion of particles having a large particle diameter is larger).Meanwhile, it is desirable that the average crystal grain size be morethan 10 μm and 20 μm or less (in the above-described range, the averagecrystal grain size be larger).

The above-described copper alloy may contain, as necessary, at least onetype of 0.005 to 0.2 percent by mass of Mg and 0.01 to 5.0 percent bymass of Zn, besides Ni, Si, and Sn. In addition, at least one type of0.01 to 0.5 percent by mass of Mn and 0.001 to 0.3 percent by mass of Crmay be contained, as necessary. It is desirable that the S content inthe above-described copper alloy be 0.02 percent by mass or less.

According to the present invention, an electric and electronic partcopper alloy sheet with excellent bending workability and stressrelaxation resistance can be obtained by using Cu—Ni—Si base copperalloys.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The alloy composition, the state of crystal grains, the state of Ni—Sidispersed particles, and the manufacturing method of a Cu—Ni—Si basecopper alloy sheet according to the present invention will bespecifically described below.

<Alloy Composition> (Ni and Si)

Nickel and Silicon are elements which generate Ni2Si dispersed particlesin a Cu—Ni—Si base copper alloy sheet and which improve the mechanicalcharacteristics of the alloy. The amount of addition of Ni is 1.5 to 4.0percent by mass, and the amount of addition of Si is specified to be anamount in accordance with the amount of addition of Ni in such a waythat a Ni/Si mass ratio becomes 4.0 to 5.0. If the amount of addition ofNi is less than 1.5 percent by mass, the mechanical characteristics aredegraded. If the amount of addition of Ni is more than 4.0 percent bymass, Ni or Si is crystallized out or precipitated in casting and thehot workability is degraded. If the Ni/Si mass ratio is less than 4.0 ormore than 5.0, excess Ni or Si makes a solid solution, so that theelectrical conductivity is degraded. The amount of addition of Ni isdesirably 1.7 to 3.6 percent by mass, further desirably 1.7 to 3.4percent by mass, and still further desirably 1.7 to 2.8 percent by mass.

(Sn)

Tin makes a solid solution with a copper alloy structure and, thereby,improves the mechanical characteristics and the stress relaxationresistance of the copper alloy. For that purpose, addition of 0.01percent by mass or more is required. On the other hand, if the amount ofaddition is more than 1.3 percent by mass, the electrical conductivityand the bending workability are degraded. Therefore, the amount ofaddition of Sn is specified to be 0.01 to 1.3 percent by mass. Theamount of addition of Sn is desirably 0.01 to 0.6 percent by mass, andfurther desirably 0.01 to 0.3 percent by mass.

(Mg)

Magnesium makes a solid solution with a copper alloy structure and,thereby, improves the mechanical characteristics and the stressrelaxation resistance of the copper alloy. For that purpose, addition of0.005 percent by mass or more is required. On the other hand, if theamount of addition is more than 0.2 percent by mass, the bendingworkability and the electrical conductivity are degraded. Therefore, theamount of addition of Mg is specified to be 0.005 to 0.2 percent bymass. The amount of addition of Mg is desirably 0.005 to 0.15 percent bymass, and further desirably 0.005 to 0.05 percent by mass.

(Zn)

Zinc improves the Sn plating releasability of the copper alloy. For thatpurpose, addition of 0.01 percent by mass or more is required. On theother hand, if the amount of addition is more than 5 percent by mass,the electrical conductivity is degraded. Therefore, the amount ofaddition of Zn is specified to be 0.01 to 5 percent by mass. The amountof addition of Zn is desirably 0.01 to 2 percent by mass, and furtherdesirably 0.01 to 1.2 percent by mass.

(Cr)

Chromium improves the hot workability of the copper alloy. For thatpurpose, addition of 0.001 percent by mass or more is required. On theother hand, if the amount of addition is more than 0.3 percent by mass,crystallized-out materials are generated and, thereby, the bendingworkability is degraded. Therefore, the amount of addition of Cr isspecified to be 0.001 to 0.3 percent by mass. The amount of addition ofCr is desirably 0.001 to 0.1 percent by mass.

(Mn)

Manganese also improves the hot workability of the copper alloy. Forthat purpose, addition of 0.01 percent by mass or more is required. Onthe other hand, if the amount of addition is more than 0.5 percent bymass, the electrical conductivity is degraded. Therefore, the amount ofaddition of Mn is specified to be 0.01 to 0.5 percent by mass. Theamount of addition of Mn is desirably 0.01 to 0.3 percent by mass.

(S)

Sulfur forms a compound with other solid solution elements and, thereby,degrade the stress relaxation resistance and the bending workability.Therefore, the S content as an incidental impurity is desirably 0.02percent by mass or less, further desirably 0.01 percent by mass or less,further desirably 0.005 percent by mass or less, and still furtherdesirably 0.002 percent by mass or less.

<State of Crystal Grains>

In general, the bending workability required of the electric andelectronic part copper alloy sheet becomes better as the average crystalgrain size is reduced. This is because the grain boundary area isreduced and segregation of solid solution elements and stressconcentration occur easily at crystal grain boundaries as the crystalgrain size increases. When the degree of stress concentration exceeds acertain level, cracking occurs from crystal grain boundaries of thecopper alloy, and intergranular cracking is reached. On the other hand,in the case where the degree of stress concentration on crystal grainboundaries is at a low level, slip occurs in a crystal grain, and in thecase of severe bending, transgranular cracking is reached. Usually,intergranular cracking has high susceptibility to cracking due tobending as compared with transgranular cracking.

Specifically, in the Cu—Ni—Si base alloy sheet according to the presentinvention, when the average crystal grain size is 20 μm or less, theform of cracking is transgranular cracking, and when the average crystalgrain size is more than 20 μm, the form of cracking is intergranularcracking. In this regard, even when the average crystal grain size is 20μm or less, in the case where particles having large particle diametersare present partly, intergranular cracking is reached. Consequently, itis necessary to reduce variations in average crystal grain size, thatis, the standard deviation 2σ of the crystal grain size. In the Cu—Ni—Sibase alloy sheet, intergranular cracking can be suppressed by specifyingthe standard deviation 2σ of the crystal grain size to be less than 10.

Meanwhile, the stress relaxation resistance required of the copper alloysheet is improved as the average crystal grain size increases. In orderto obtain good stress relaxation resistance suitable for an electric andelectronic part copper alloy sheet, it is necessary that the averagecrystal grain size is 5 μm or more.

In consideration of the above-described influences of the crystal grainsize on the bending workability and the stress relaxation resistance ofthe copper alloy sheet, in order to allow the copper alloy sheet to haveboth the above-described characteristics, it is desirable that theaverage crystal grain size of the copper alloy sheet be within the rangein which intergranular cracking can be suppressed and the crystal grainsize be maximized within that range. That is, the average crystal grainsize is 5 to 20 μm and the standard deviation 2σ of the crystal grainsize is less than 10. The average crystal grain size is within the rangeof desirably 7 to 20 μm, and further desirably more than 10 μm.

<State of Ni—Si Dispersed Particles>

The present inventors examined the bending workability and the stressrelaxation resistance of a Cu—Ni—Si base copper alloy sheet subjected toa Ni—Si particle precipitation treatment before a recrystallizationtreatment accompanied by a solution treatment (refer to a manufacturingmethod described later). As a result, it was made clear that in thecopper alloy sheet having these characteristics satisfying desiredvalues, many Ni—Si particles having a particle diameter of 30 to 300 nmwere precipitated (within the range of about 50 to 500 particles/100μm²), and among them, the proportion of the number of particles having aparticle diameter of 90 nm or more was 20% or more. In the copper alloysheet with particularly excellent bending workability and stressrelaxation resistance, the proportion of the number of particles havinga particle diameter of 120 nm or more was 30% or more in Ni—Si dispersedparticles having a particle diameter of 30 to 300 nm.

In recrystallization treatment accompanied by a solution treatment,growth of recrystallized grains is controlled by sustaining the Ni—Sidispersed particles having a particle diameter of 30 to 300 nm remain ina base material after the recrystallization treatment accompanied by asolution treatment. In the case where the proportion of the number ofparticles having a particle diameter of 90 nm or more in Ni—Si dispersedparticles having a particle diameter of 30 to 300 nm is 20% or more orthe proportion of the number of particles having a particle diameter of120 nm or more is 30% or more, a phenomenon in which, inrecrystallization treatment accompanied by a solution treatment, thegrowth rate increases sharply, when recrystallized grains are grown andexceed a predetermined dimension, is relaxed, so that the grain size andthe standard deviation of the recrystallized grains are controlledeasily.

<Manufacturing Method>

A previously employed standard method for manufacturing a Cu—Ni—Si basecopper alloy sheet having the composition according to the presentinvention includes melting and casting→soaking treatment→hotrolling→quenching after hot rolling→cold rolling→recrystallizationtreatment accompanied by solution treatment→cold rolling→agingtreatment. In addition, the steps performed in the order of agingtreatment→cold rolling after the recrystallization treatment accompaniedby a solution treatment is effective for enhancing strength.Furthermore, in order to obtain a better spring property,low-temperature annealing may be performed finally.

Meanwhile, in order to obtain the copper alloy sheet according to thepresent invention, it is necessary to perform precipitation treatment ofNi—Si dispersed particles at a stage before the recrystallizationtreatment accompanied by a solution treatment. Specifically, besides theindividual steps of the previously employed standard manufacturingmethod described above, at least one precipitation step to precipitateNi—Si dispersed particles may be added at an appropriate stage afterstart of the hot rolling and before the solution treatment accompaniedby recrystallization.

Precipitates generated in the aging treatment after the solutiontreatment are fine and, in general, particle diameters are severalnanometers to 20 nm. On the other hand, crystallized-out materials arecoarse and, in general, most of them have particle diameters of morethan 1,000 nm. Therefore, all or most of Ni—Si dispersed particles whichare observed in the final copper alloy sheet and which have particlediameters of 30 to 300 nm are precipitated in the precipitation stepbefore the recrystallization treatment accompanied by a solutiontreatment.

Each of the steps of the above-described manufacturing method will bedescribed in more detail.

(Soaking Treatment and Hot Rolling)

The soaking treatment is performed under the condition of holding at atemperature of 850° C. to 1,000° C. for 0.2 to 16 hours. Subsequently,the hot rolling is performed.

(Precipitation Treatment of Ni—Si Dispersed Particles)

In the precipitation treatment, for example, (1) hot rolling is finishedat 700° C. or higher and, thereafter, slow cooling from 700° C. to 200°C. is performed at an average cooling rate of 100° C./hr or less or (2)hot rolling is finished at 700° C. or higher, water cooling (the rate ofcooling to 300° C. is specified to be 400° C./min or more) is performedand, thereafter, heating is performed at a temperature of higher than500° C. and 700° C. or lower, desirably higher than 550° C. and 700° C.or lower, and further desirably higher than 600° C. and 700° C. or lowerfor 1 minute to 20 hours before the recrystallization treatmentaccompanied by a solution treatment is performed. In either case, Ni—Sidispersed particles remaining after the recrystallization treatmentaccompanied by a solution treatment are precipitated by thisprecipitation treatment.

In order to achieve the crystal grain structure and the Ni—Si dispersionstate according to the present invention, it is desirable that, in thisprecipitation treatment step, Ni—Si dispersed particles be precipitatedinto the base material uniformly. In the case where the method of theabove-described item (2) is employed, it is desirable that the rate oftemperature raising to a temperature of 500° C. or higher and 700° C. orlower be constant.

(Cold Rolling)

A copper alloy sheet having a predetermined sheet thickness by this coldrolling is subjected to the recrystallization treatment accompanied by asolution treatment at that sheet thickness. The sheet thickness of therecrystallization treatment accompanied by a solution treatment isdetermined on the basis of the product sheet thickness and a coldrolling reduction ratio after the recrystallization treatmentaccompanied by a solution treatment. This cold rolling may be performedbefore or after the above-described precipitation treatment.

(Recrystallization Treatment Accompanied by Solution Treatment)

The purposes of the recrystallization treatment accompanied by asolution treatment are to dissolve Ni and Si as a solid solution at astage before the aging treatment and form a recrystallization structurehaving good bending workability and stress relaxation resistance. Thefavorable condition of the recrystallization treatment accompanied by asolution treatment is influenced by the Ni and Si contents in the copperalloy and the precipitation condition of the upstream step. In the casewhere the Ni and Si contents are small, a lower temperature isfavorable, and in the case where the Ni and Si contents are large, ahigher temperature is favorable. Meanwhile, when the precipitationcondition is a long time, a high temperature is favorable, and when theprecipitation condition is a short time, a low temperature is favorable.Specifically, selection may be performed from the condition of holdingat a temperature of 700° C. to 900° C. for 5 to 300 seconds. In thisrecrystallization treatment accompanied by a solution treatment, Ni—Sidispersed particles which have been precipitated exert a pinning effectduring the recrystallization treatment and remain after therecrystallization treatment. As the condition of the recrystallizationtreatment accompanied by a solution treatment becomes a low temperatureor a short time, the average crystal grain size becomes small and thebending workability is improved. Conversely, as the condition becomes ahigh temperature or a long time, the amount of solid solution of Ni andSi increases so as to enhance the strength characteristics of a productsheet, and the average crystal grain size increases so as to improve thestress relaxation resistance.

(Cold Rolling)

The cold rolling after the recrystallization treatment accompanied by asolution treatment is performed under the condition of the reductionratio of 10% to 50%. Nucleation sites of precipitates are introduced bythe cold rolling. If the cold rolling reduction ratio is more than 50%,the bending workability is degraded.

(Precipitation Treatment)

The precipitation treatment is performed at 350° C. to 500° C. for 30minutes to 24 hours. If the holding temperature is lower than 350° C.,precipitation of Ni2Si becomes insufficient. If the holding temperatureis higher than 500° C., the strength of the copper alloy sheet isreduced, and required strength characteristics is not obtained.Meanwhile, if the holding time is less than 30 minutes, precipitation ofNi2Si becomes insufficient, and if the holding time is more than 24hours, the productivity is impaired.

In the manufacturing method described above, the cold rolling and therecrystallization treatment accompanied by a solution treatment may beperformed repeatedly after the hot rolling, final cold rolling may beperformed after the aging treatment, or low-temperature annealing may beperformed as a final step. In the case where cold rolling is performedafter the aging treatment, it is desirable that a total of the reductionratio thereof and the reduction ratio of the cold rolling before theaging treatment be 50% or less.

EXAMPLES

Copper alloys having compositions of Nos. 1 to 5 shown in Tables 1 and 2were melted and cast with a kryptol furnace in the air under coverage bycharcoal. An ingot was subjected to a soaking treatment under thecondition of 800° C. to 1,000° C. for 1 to 3 hours and, subsequently,hot rolling was finished at 700° C. or higher. Then, Nos. 1 to 28 and 33to 48 were water-cooled promptly. Nos. 29 to 32 were quenched at anaverage cooling rate of 100° C./hr or less. Nos. 49 and 50 were quenchedto 500° C. at a cooling rate of 50° C./min, were held at 500° C. for 2hours, and were water-cooled to room temperature. As results of thesetreatments, hot-rolled sheets having a thickness of 20 mm were obtained.In this regard, as for No. 33, cracking occurred in the hot rolling, sothat a hot-rolled sheet was not obtained and the steps thereafter werecancelled.

Both surfaces of the resulting hot-rolled sheet were cut by 1 mm so asto adjust the sheet thickness to be 18 mm, and cold rolling wasperformed at an appropriate reduction ratio (including 0%).Subsequently, Nos. 1 to 25, 34 to 43, and 47 to 48 were heated to atemperature of higher than 600° C. and 700° C. or lower at 0.5° C. to10° C./min and Nos. 26 to 28 were heated to a temperature of higher than500° C. and 600° C. or lower at 0.5° C. to 10° C./min. Holding for 5 to20 hours was performed. After the holding for a predetermined time,Ni—Si dispersed particles were precipitated by cooling in the furnace.In this regard, as for Nos. 29 to 32, Ni—Si dispersed particles wereprecipitated by slow cooling after the hot rolling. Nos. 44 to 46 werenot subjected to a precipitation treatment before the recrystallizationtreatment.

TABLE 1 Alloy composition (percent by mass) No. Cu Ni Si Sn Zn Mg Cr MnS Ni/Si 1 Example remainder 1.5 0.35 0.10 0.00 0.000 0.000 0.00 0.0024.3 2 remainder 1.8 0.40 0.10 0.00 0.000 0.000 0.00 0.002 4.5 3remainder 2.5 0.55 0.10 0.00 0.000 0.000 0.00 0.002 4.5 4 remainder 3.60.80 0.10 0.00 0.000 0.000 0.00 0.002 4.5 5 remainder 3.2 0.70 0.10 0.000.000 0.000 0.00 0.002 4.6 6 remainder 3.2 0.64 0.10 0.00 0.000 0.0000.00 0.002 5.0 7 remainder 3.2 0.80 0.10 0.00 0.000 0.000 0.00 0.002 4.08 remainder 3.2 0.70 0.01 0.00 0.000 0.000 0.00 0.002 4.6 9 remainder2.0 0.45 0.50 0.00 0.000 0.000 0.00 0.002 4.4 10 remainder 2.5 0.55 1.300.00 0.000 0.000 0.00 0.002 4.5 11 remainder 1.8 0.40 0.10 0.01 0.0000.000 0.00 0.002 4.5 12 remainder 2.7 0.60 0.10 0.10 0.000 0.000 0.000.002 4.5 13 remainder 3.2 0.70 0.10 1.00 0.000 0.000 0.00 0.002 4.6 14remainder 2.5 0.55 0.10 5.00 0.000 0.000 0.00 0.002 4.5 15 remainder 3.00.65 0.10 0.00 0.005 0.000 0.00 0.002 4.6 16 remainder 1.8 0.40 0.100.00 0.050 0.000 0.00 0.002 4.5 17 remainder 2.0 0.45 0.10 0.00 0.2000.000 0.00 0.002 4.4 18 remainder 2.5 0.55 0.10 0.00 0.000 0.001 0.000.002 4.5 19 remainder 2.3 0.50 0.10 0.00 0.000 0.030 0.00 0.002 4.6 20remainder 2.7 0.60 0.10 0.00 0.000 0.300 0.00 0.002 4.5 21 remainder 3.20.70 0.10 0.00 0.000 0.000 0.01 0.002 4.6 22 remainder 3.0 0.65 0.100.00 0.000 0.000 0.10 0.002 4.6 23 remainder 2.7 0.60 0.10 0.10 0.0000.000 0.00 0.02 4.5 24 remainder 1.8 0.40 0.10 0.00 0.000 0.000 0.500.002 4.5 25 remainder 2.5 0.55 0.10 1.00 0.050 0.030 0.10 0.002 4.5 26remainder 2.7 0.60 0.10 0.10 0.000 0.000 0.00 0.002 4.5 27 remainder 2.50.55 0.10 0.00 0.000 0.000 0.00 0.002 4.5 28 remainder 3.0 0.65 0.100.00 0.005 0.000 0.00 0.002 4.6 29 remainder 1.8 0.40 0.10 0.00 0.0000.000 0.00 0.002 4.5 30 remainder 3.2 0.70 0.10 0.00 0.000 0.000 0.000.002 4.6 31 remainder 2.0 0.45 0.50 0.00 0.000 0.000 0.00 0.002 4.4 32remainder 2.5 0.55 0.10 0.00 0.000 0.001 0.00 0.002 4.5

TABLE 2 Alloy composition (percent by mass) No. Cu Ni Si Sn Zn Mg Cr MnS Ni/Si 33 Comparative remainder 4.5* 1.00 0.10 0.00 0.000 0.000 0.000.002 4.5 34 example remainder 1.2* 0.25 0.10 0.00 0.000 0.000 0.000.002 4.8 35 remainder 3.2 1.00 0.10 0.00 0.000 0.000 0.00 0.002 3.2* 36remainder 3.2 0.60 0.10 0.00 0.000 0.000 0.00 0.002 5.3* 37 remainder1.8 0.40 0.00* 0.00 0.000 0.000 0.00 0.002 4.5 38 remainder 3.0 0.651.50* 0.00 0.000 0.000 0.00 0.002 4.6 39 remainder 2.5 0.55 0.10 8.00*0.000 0.000 0.00 0.002 4.5 40 remainder 2.3 0.50 0.10 0.00 0.300* 0.0000.00 0.002 4.6 41 remainder 2.7 0.60 0.10 0.00 0.000 0.500* 0.00 0.0024.5 42 remainder 3.2 0.70 0.10 0.00 0.000 0.000 1.00* 0.002 4.6 43remainder 1.8 0.40 0.10 0.00 0.010 0.000 0.00 0.03* 4.5 44 remainder 2.30.50 0.10 0.00 0.000 0.030 0.00 0.002 4.6 45 remainder 2.7 0.60 0.100.10 0.000 0.000 0.00 0.002 4.5 46 remainder 3.2 0.70 0.10 0.00 0.0000.000 0.00 0.002 4.6 47 remainder 2.7 0.60 0.10 0.10 0.000 0.000 0.000.002 4.5 48 remainder 2.7 0.60 0.10 0.10 0.000 0.000 0.00 0.002 4.5 49remainder 1.8 0.40 0.10 1.10 0.020 0.000 0.02 0.002 4.5 50 remainder 3.20.70 0.00* 0.00 0.000 0.020 0.00 0.002 4.6 *asterisked values are out ofthe specification of the present invention

After an oxide film of the sheet was removed with emery paper, coldrolling was performed so as to adjust the sheet thickness to be 0.3 to0.2 mm.

Subsequently, Nos. 1 to 32, 34 to 46, 49, and 50 were held at atemperature of 700° C. to 900° C. for within the range of 5 to 300seconds, No. 47 was held at a temperature of lower than 700° C. forwithin the range of 5 to 300 seconds, and No. 48 was held at atemperature of higher than 900° C. for within the range of 5 to 300seconds. Thereafter, recrystallization treatment accompanied by asolution treatment was performed by quenching in water.

Final cold working was performed so as to obtain a material having asheet thickness of 0.15 mm, and a precipitation treatment was performedat 430° C. to 480° C. for 2 hours.

Specimens were cut from the copper alloy sheets of Nos. 1 to 32 and 34to 50 produced by the above-described steps, and a 0.2% proof stressmeasurement on the basis of a tensile test, an electrical conductivitymeasurement, a W-bending test, observation and measurement of thecrystal structure, observation and measurement of dispersed particles,and stress relaxation resistance examination were performed in thefollowing manners. The results thereof are shown in Tables 3 and 4.

<Tensile Test>

A JIS No. 5 specimen in which the rolling direction was a longitudinaldirection was used, and a tensile test in conformity with JIS Z2241 wasperformed so as to determine the 0.2% proof stress. In examples at thattime, a 0.2% proof stress of 550 N/mm² or more was accepted.

<Electrical Conductivity Measurement>

A specimen 10 mm wide by 300 mm long, in which the rolling direction wasa longitudinal direction, was used, the electric resistance was measuredwith a double bridge type electric resistance measuring apparatus inconformity with the measuring method for electrical conductivity ofnon-ferrous materials described in JIS H0505, and the electricalconductivity was calculated by an average cross-sectional area method.In examples at that time, an electrical conductivity of 35%IACS or morewas accepted.

<W-Bending Test>

Specimens 10 mm wide by 30 mm long, in which L. D. (parallel to therolling direction) or T.D. (perpendicular to the rolling direction) wasa longitudinal direction, were used, and the W-bending test wasperformed, where bending radius R was specified to be 0.05 mm, inconformity with the W-bending test described in JCBA T307. After theW-bending test, an observation surface in a direction perpendicular to abending axis was obtained by using a cold embedding resin, finishpolishing was performed with No. 2400 count waterproof abrasive paperand a buff coated with 1-μm diamond spray. In addition, crystal grainboundaries were corroded with chromic acid and ferric chloride and,thereby, an observation sample was obtained. A bending vertex of theobservation sample was observed, and presence or absence of cracking andthe form of cracking of each of the three samples were examined. Thecase where cracking was not observed was evaluated as ◯ (acceptable) andthe case where cracking was observed was evaluated as × (notacceptable).

<Measurement of Average Crystal Grain Size>

An observation surface defined by a rolling direction and a sheetthickness direction was obtained by using a cold embedding resin and,thereafter, finish polishing was performed with No. 2400 countwaterproof abrasive paper and a buff coated with 1-diamond spray. Inaddition, crystal grain boundaries were corroded with chromic acid andferric chloride and, thereby, an observation sample was obtained. Anoptical microscope was used for structural observation and a structuralphotograph was obtained under a magnification of 400 times. A cuttingmethod was used for measuring the average crystal grain size, fourlines, each having a length of 250 μm, were drawn on the structuralphotograph, where the direction of the line was specified to be adirection parallel to the rolling direction, and an arithmetic averageof crystal grain sizes determined with respect to the respective lineswas specified to be an average crystal grain size.

<Measurement of Standard Deviation of Crystal Grain Size>

A field emission scanning electron microscope equipped with abackscattered electron diffraction image system produced by TSL wasused, and the measurement was performed by a crystal orientationanalysis method. Electron beams were applied to a measurement area of100 by 100 μm in steps of 0.4 μm, and a crystal orientation differenceof 15° or more was considered as a crystal grain boundary. An area ofeach crystal grain in the area was measured, and the equivalent circlediameter thereof was considered as the crystal grain size. The standarddeviation a of the crystal grain size was determined on the basis of thefollowing Formula (1), where the number of measured crystal grains wasspecified to be n and the individual crystal grain sizes were specifiedto be Da (a=1, 2, 3, . . . , n).

$\begin{matrix}{\sigma = \frac{\sqrt{\sum\limits_{a = 1}^{n}\left( {D_{a} - \frac{\sum\limits_{a = 1}^{n}D_{a}}{n}} \right)^{2}}}{n - 1}} & (1)\end{matrix}$

<Observation of Dispersed Particles>

A cross section defined by the rolling direction and the sheet thicknessdirection was produced by ion milling, and observation was performed byusing the field emission scanning electron microscope under amagnification of 15,000 times. The number of dispersed particles of 30to 300 nm in a region of 100 μm² of each sample was measured. Thediameters and frequencies of appearance thereof were examined, and amongthe dispersed particles having a diameter of 30 to 300 nm, theproportion of the number of particles having a particle diameter of 90to 300 nm and the proportion of the number of particles having aparticle diameter of 120 to 300 nm were determined. In the presentinvention, the particle diameter of the dispersed particle refers to amajor axis (maximum length) of the particle.

<Stress Relaxation Resistance Measurement>

The measurement of the stress relaxation resistance was performed by acantilever system in conformity with the Electronic MaterialsManufacturers Association Standard EMAS01011. A strip specimen 10 mmwide by 60 mm long, in which a longitudinal direction was a directionperpendicular to the rolling direction, was used.

The above-described specimen was used. The specimen was fixed to a jig,where the span length was set in such a way that the load stress became80% of the 0.2% proof stress on the basis of Formula (2) describedbelow.

d=0.8×σ_(0.2) ×l ²/(1.5×E×t)   (2)

where d: initial set (mm), σ_(0.2): proof stress (N/mm²), l: span length(mm), E: deflection factor (N/mm²), and t: sheet thickness (mm).

The specimen in the state of being fixed to the jig was heated in anoven at 150° C. for 1,000 hours. After the heating, the load stress wasremoved from the specimen, the deflection δ (mm) after removal of theload stress was measured, and the stress relaxation ratio RS (%) wascalculated on the basis of Formula (3) described below. In examples atthat time, a stress relaxation ratio of 15% or less was accepted.

RS=100×δ/d   (3)

As shown in Tables 3 and 4, Nos. 1 to 32, in which the alloycomposition, the average crystal grain size, the standard deviation ofthe crystal grain size, and the particle diameter distribution of Ni—Sidispersed particles satisfied the specifications according to thepresent invention, were superior in all the 0.2% proof stress, theelectrical conductivity, the bending workability, and the stressrelaxation resistance. The number of dispersed particles having aparticle diameter of 30 to 300 nm of each of Nos. 1 to 32 was within therange of 50 to 100 in 100 μm².

Meanwhile, as for Nos. 33 to 43 in which the alloy composition did notsatisfy the specification according to the present invention and Nos. 44to 50 in which at least one of the average crystal grain size, thestandard deviation of the crystal grain size, and the particle diameterdistribution of Ni—Si dispersed particles did not satisfy thespecifications according to the present invention, at least onecharacteristic of the 0.2% proof stress, the electrical conductivity,the bending workability, and the stress relaxation resistance was poor.

Specifically, No. 33 had an excessive Ni content, and cracking occurredin hot rolling, so that it was not possible to produce a specimen. No.34 had a small 0.2% proof stress because the Ni content were too small.No. 35 had a small Ni/Si ratio, No. 36 had a high Ni/Si ratio, and bothhad low electrical conductivity. No. 37 did not contain Sn, and thestress relaxation ratio was high. Nos. 38, 40, and 41 containedexcessive Sn, Mg, and Cr, respectively, and all had low electricalconductivity and poor bending workability. No. 39 contained excessiveZn, the electrical conductivity was low, and the stress relaxation ratiowas high. No. 42 contained excessive Mn, and the electrical conductivitywas low. No. 43 contained excessive S which was an incidental impurity,the bending workability was poor, and the stress relaxation ratio washigh.

TABLE 3 Average Standard Proportion of 0.2% Stress crystal deviationdispersed particles Proof Electrical W-bending relaxation grain size 2σ90-300 nm 120-300 nm stress conductivity test resistance No. [μm] [μm][%] [%] [Mpa] [% IACS] L.D. T.D. [%] 1 Example 12 8.0 85 60 560 45 ◯ ◯15 2 10 7.0 83 60 580 44 ◯ ◯ 14 3 15 7.5 75 50 650 40 ◯ ◯ 14 4 13 7.0 7044 710 39 ◯ ◯ 13 5 12 7.0 78 50 700 40 ◯ ◯ 13 6 11 6.5 75 45 690 37 ◯ ◯13 7 17 8.2 80 55 710 37 ◯ ◯ 13 8 17 8.0 80 50 680 42 ◯ ◯ 15 9 10 6.5 7648 640 38 ◯ ◯ 12 10 7 6.0 81 52 700 35 ◯ ◯ 10 11 15 7.2 82 51 580 43 ◯ ◯14 12 15 7.5 84 55 660 40 ◯ ◯ 14 13 14 7.7 77 50 700 38 ◯ ◯ 14 14 16 8.075 45 640 36 ◯ ◯ 15 15 15 7.6 81 53 680 40 ◯ ◯ 13 16 13 7.0 76 48 600 38◯ ◯ 11 17 12 6.8 78 50 620 36 ◯ ◯ 9 18 15 7.0 80 52 650 40 ◯ ◯ 14 19 167.5 82 53 640 39 ◯ ◯ 14 20 13 7.0 86 60 680 37 ◯ ◯ 14 21 14 7.2 74 48700 40 ◯ ◯ 14 22 13 7.0 70 45 680 39 ◯ ◯ 13 23 15 7.2 80 50 660 40 ◯ ◯15 24 15 8.0 78 50 590 37 ◯ ◯ 12 25 10 6.8 78 50 670 36 ◯ ◯ 10 26 9 7.023 12 630 40 ◯ ◯ 15 27 9 7.5 50 29 630 40 ◯ ◯ 15 28 8 6.8 65 35 660 40 ◯◯ 14 29 13 8.0 85 65 570 44 ◯ ◯ 12 30 14 8.5 80 60 680 40 ◯ ◯ 12 31 127.2 82 59 620 39 ◯ ◯ 11 32 16 7.6 86 62 640 40 ◯ ◯ 12

TABLE 4 Average crystal Standard Proportion of 0.2% Stress graindeviation dispersed particles Proof Electrical W-bending relaxation size2σ 90-300 nm 120-300 nm stress conductivity test resistance No. [μm][μm] [%] [%] [Mpa] [% IACS] L.D. T.D. [%] 33 Comparative occurrence ofcracking 34 example 15 7.0 77 50 520* 45 ◯ ◯  16* 35  8 6.0 85 62 670 33* ◯ ◯ 13 36 16 6.6 83 54 690  33* ◯ ◯ 13 37 17 8.0 75 49 560 45 ◯ ◯ 17* 38  6 6.0 78 50 750  33* X X  9 39 13 7.0 80 51 650  34* ◯ ◯  17*40 10 6.7 76 48 680  34* X X  8 41 12 7.0 85 58 700  34* X X 12 42 158.0 82 53 720  33* ◯ ◯ 12 43 15 7.5 80 51 580 43 X X  16* 44 10 13.0* 10*  4* 680 39 X X 14 45  9 12.5*  12*  5* 720 40 X X 14 46  7 12.1* 15*  7* 730 40 X X 13 47  4* 4.0 80 52 560 42 ◯ ◯  21* 48  55* 18.0*measurement 700 37 X X 10 was impossible 49  3* 4.2  13*  7* 560 44 ◯ ◯ 20* 50  4* 4.5  17*  10* 720 50 ◯ ◯  22* *asterisked values are out ofthe specification of the present invention or inferior incharacteristics

As for each of Nos. 44 to 46 in which a precipitation treatment of Ni—Sidispersed particles was not performed before the recrystallizationtreatment accompanied by a solution treatment, the standard deviation ofthe crystal grain size was larger than that in the specification, theproportion of the number of particles having a particle diameter of 90to 300 nm and the proportion of the number of particles having aparticle diameter of 120 to 300 nm were small, and the bendingworkability was poor.

The temperature of recrystallization treatment accompanied by a solutiontreatment of No. 47 was too low. Therefore, the average crystal grainsize was smaller than that in the specification, and the stressrelaxation ratio was high. The temperature of recrystallizationtreatment accompanied by a solution treatment of No. 48 was too high.Therefore, the average crystal grain size and the standard deviation ofthe crystal grain size were larger than those in the specification,dispersed particles of 30 to 300 nm were not observed, and the bendingworkability was poor. In No. 48, intergranular cracking occurred.

The method described in Japanese Patent Application Publication No.2008-196042 was applied to Nos. 49 and 50. The proportion of the numberof particles having a particle diameter of 90 to 300 nm and theproportion of the number of particles having a particle diameter of 120to 300 nm were small, the average crystal grain size was smaller thanthat in the specification, and the stress relaxation ratio was high.

1. A copper alloy sheet, comprising: Cu; 1.5 to 4.0 percent by mass ofNi; Si satisfying a Ni/Si mass ratio of 4.0 to 5.0; and 0.01 to 1.3percent by mass of Sn, wherein the copper alloy sheet has an averagecrystal grain size of 5 to 20 μm and a standard deviation of a crystalgrain size satisfying 2σ<10 μm, and a proportion of particles having aparticle diameter of 90 to 300 nm in Ni—Si dispersed particles having aparticle diameter of 30 to 300 nm is 20% or more when the particles areobserved in a cross-section defined by a direction perpendicular to asheet surface and a direction parallel to a rolling direction.
 2. Thecopper alloy sheet according to claim 1, wherein a proportion ofparticles having a particle diameter of 120 to 300 nm in the Ni—Sidispersed particles is 30% or more when the particles are observed inthe cross-section.
 3. The copper alloy sheet according to claim 1,wherein the copper alloy sheet has an average crystal grain size of morethan 10 μm and 20 μm or less.
 4. The copper alloy sheet according toclaim 1, wherein the copper alloy sheet further comprises 0.005 to 0.2percent by mass of Mg.
 5. The copper alloy sheet according to claim 1,wherein the copper alloy sheet further comprises 0.01 to 5.0 percent bymass of Zn.
 6. The copper alloy sheet according to claim 1, wherein thecopper alloy sheet further comprises at least one type selected from thegroup consisting of 0.01 to 0.5 percent by mass of Mn and 0.001 to 0.3percent by mass of Cr.
 7. The copper alloy sheet according to claim 1,wherein the copper alloy sheet comprises a S content of 0.02 percent bymass or less.
 8. The copper alloy sheet according to claim 4, whereinthe copper alloy sheet further comprises 0.01 to 5.0 percent by mass ofZn.
 9. The copper alloy sheet according to claim 4, wherein the copperalloy sheet further comprises at least one type selected from the groupconsisting of 0.01 to 0.5 percent by mass of Mn and 0.001 to 0.3 percentby mass of Cr.
 10. The copper alloy sheet according to claim 5, whereinthe copper alloy sheet further comprises at least one type selected fromthe group consisting of 0.01 to 0.5 percent by mass of Mn and 0.001 to0.3 percent by mass of Cr.
 11. The copper alloy sheet according to claim4, wherein the copper alloy sheet comprises a S content of 0.02 percentby mass or less.
 12. The copper alloy sheet according to claim 5,wherein the copper alloy sheet comprises a S content of 0.02 percent bymass or less.
 13. The copper alloy sheet according to claim 6, whereinthe copper alloy sheet comprises a S content of 0.02 percent by mass orless.
 14. The copper alloy sheet according to claim 1, wherein thecopper alloy sheet is suitable for an electric part.
 15. The copperalloy sheet according to claim 1, wherein the copper alloy sheet issuitable for an electronic part.